The U.S. Supreme Court on Monday refused to block a lower court ruling requiring Republican-drawn congressional districts in Pennsylvania to be reworked immediately, boosting Democratic hopes of winning control this year of the U.S. House of Representatives.

Justice Samuel Alito denied an emergency application filed by Republicans to stop the immediate reworking of the electoral district boundaries, preserving a ruling by the state’s top court that they had unlawfully sought partisan advantage over the Democrats in drawing the maps.

The Jan. 22 Pennsylvania Supreme Court ruling gives Republican legislators until this Friday to submit a revised map to Democratic Governor Tom Wolf, who would have until Feb. 15 to sign off on the changes. If those deadlines pass without an agreement, the state court said it would rewrite the map itself.

Democrats, who hold only five of Pennsylvania’s 18 congressional districts despite its status as a closely divided electoral swing state, must capture at least two dozen seats currently held by Republicans in the Nov. 6 congressional mid-term elections to wrest control of the U.S. House.

A new map potentially could give Democratic candidates a chance to pick up several Republican-held seats in Pennsylvania alone, with national polls showing voters strongly favoring Democrats in 2018.

The Pennsylvania fight is one of several across the United States focusing on what is known as partisan gerrymandering, the manipulation of the composition of legislative districts to amplify the voting power of one party at the expense of another.

The Pennsylvania court ruled that the state’s electoral maps had been crafted by the Republicans who controlled the state legislature in a way that violated the state’s constitution by diluting the electoral influence of Democratic votes.

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